package class03;

import sun.java2d.pipe.AAShapePipe;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class BiggerThanRightTwice2 {
    public static int reversePairs(int[] arr) {
        if (arr == null || arr.length < 2)
            return 0;
        return process(arr, 0, arr.length - 1);
    }

    public static int process(int[] arr, int L, int R) {
        if (L == R)
            return 0;
        int mid = L + ((R - L) >> 1);
        return process(arr, L, mid)
                + process(arr, mid + 1, R)
                + merge(arr, L, mid, R);
    }

    public static int merge(int[] arr, int L, int M, int R) {
        int res = 0;
        int p0 = M + 1;
        for (int i = L; i <= M; i++) {
            while (p0 <= R && arr[i] > arr[p0] * 2)
                p0++;
            res += p0 - M - 1;
        }

        int[] help = new int[R - L + 1];
        int i = 0;
        int p1 = L;
        int p2 = M + 1;
        while (p1 <= M && p2 <= R)
            help[i++] = arr[p1] <= arr[p2] ? arr[p1++] : arr[p2++];
        while (p1 <= M)
            help[i++] = arr[p1++];
        while (p2 <= R)
            help[i++] = arr[p2++];
        for (i = 0; i < help.length; i++)
            arr[L + i] = help[i];
        return res;
    }

    public static int comparator(int[] arr) {
        if (arr == null || arr.length < 2)
            return 0;
        int res = 0;
        for (int i = 0; i < arr.length; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[i] > arr[j] * 2)
                    res++;
            }
        }
        return res;
    }

    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) ((maxValue + 1) * Math.random());
        }
        return arr;
    }

    public static int[] copyArray(int[] arr) {
        if (arr == null)
            return null;
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++)
            res[i] = arr[i];
        return res;
    }

    public static boolean isEqual(int[] arr1, int[] arr2) {
        if ((arr1 != null && arr2 == null) || (arr1 == null && arr2 != null))
            return false;
        if (arr1 == null && arr2 == null)
            return true;
        if (arr1.length != arr2.length)
            return false;
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i])
                return false;
        }
        return true;
    }

    public static void printArray(int[] arr) {
        if (arr == null)
            return;
        for (int i = 0; i < arr.length; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }

    public static void main(String[] args) {
        int testTime = 500000;
        int maxSize = 100;
        int maxValue = 100;
        System.out.println("test begin!");
        for (int i = 0; i < testTime; i++) {
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);
            if (reversePairs(arr1) != comparator(arr2)) {
                System.out.println("Oops!");
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println("test end!");
    }
}
